Mold for the centrifugal casting of metal cylinders



1966 SHUNGO KAWABATA 3,

MOLD FOR THE CENTRIFUGAL CASTING OF METAL CYLINDERS Filed July 31, 1963 FIG.

FIG.2

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INVENTOR Kn we be Ta BY {Ma/6% M Shungo ATTORNEY5 United States Patent Ofitice 3,292,219 Patented Dec. 20, 1966 Y 3,292,219 V MOLD FOR THE CENTRIFUGAL CASTING F METAL CYLINDERS Shuugo Kawabata, Ashiya, Hyogo Prefecture, Japan, as-

signor of one-half to Yawata Iron & Steel Co., Ltd., Tokyo, Japan, a corporation of Japan Filed July 31, 1963, Ser. No. 298,864 4 Claims. (Cl. 22-1135) This invention relates to the improvement in general of the centrifugal casting of metal cylinders, and particularly to the centrifugal casting of metal cylinders by using a metal flask lined with a particular shape of a premolded sand mold of a sand bonded with thermo-setting resin.

An object of this invention is to provide a centrifugal casting mold which is capable of producing metal cylinders having a smooth surface and an accurate shape and size, this capacity being attained by using a cylinder of sand consisting of thermo-setting resin and silica sand which has been pro-molded and inserted into the flask.

Another object of this invention is to provide a centrifugal casting mold which is capable of producing metal cylinders of good quality at a high productivity rate and of making the molding process simpler and easier, this capacity being attained by using a cylinder of sand mold material consisting of thermo-setting resin and silica sand which has been pre-molded and inserted into the flask.

Another object of this invention is to provide a centrifugal casting mold which is so improved as to enable one to use a simpler mechanism molding machine, reducing the equipment cost, this advantage being obtained by using a cylinder of sand mold material consisting of thermosetting resin and silica sand which has been pre-molded and inserted into the flask.

Other objects and a fuller understanding of this invention will be made clear by reference to the following specification and accompanying drawings, in which FIG. 1 is a longitudinal sectional view of a cylinder of sand according to the present invention;

FIG. 2 is a transverse sectional view of the cylinder of sand of FIG. 1;

FIG. 3 is a longitudinal sectional view of a centrifugal casting mold with the cylinder of sand of FIG. 1 in position therein; and

FIG. 4 is a transverse sectional view of the centrifugal casting mold of FIG. 3.

There have been numerous inventions and improvements in methods and apparatus for the centrifugal casting of metal cylinders, among which the most advanced is a method of using a sand mold consisting of thermosetting resing and sand which is formed inside the cylindrical metal flask. According to this method, a mixture of a thermo-setting resin such as phenolic resin and silica in the form of molding sand is sprayed into the inside of the cylindrical metal flask. This mixture will instantly melt and solidify to form a sand layer (i.e., a sand mold) adhering to the whole of the inside of the metal flask because the rotating mold is preheated to about 150 C. The thickness of the sand layer is 5-10 mm. Centrifugal casting is carried out by using this sand layer as a sand -mold. The merits of this method are that a sand mold is made instantly. On the other hand, this method has the drawback that the exposed surface of the sand layer adhering to the inside of the metal flask is not smooth but rough, so that the surface of a metal cylinder produced by using such sand layer in the sand mold will also be rough and uneven. This is because almost no means is available to use a pattern to smooth the surface of the layer when the resin-sand mixture is sprayed into the inside of the metal flask, and the resin melts, solidifies and adheres to the inside of the flask. Thus, there is formed a rough and uneven surface on the sand layer. This is the greatest drawback of said method, which cannot be overcome otherwise than by the present invention. This drawback can be overcome by this invention by first forming a cylinder of sand (hereafter called the sand cylinder) consisting of therm-o-setting resin and sand, by using a metal pattern on both the inside and outside so as to form a smooth, accurate surface, and the cylinder is pushed or inserted into the metal flask, and this combination is used as the centrifugal casting mold and is capable of producing metal cylinders having a smooth, accurate surface and at a high rate of productivity.

A comparison between the sand layer consisting of thermo-setting resin and sand fused on and adhering to the inside of the metal flask, and the old type of baked sand mold using sand and clay is shown below. The former is much greater than the latter in both tensile and compressive strength:

The process of this invention is to prepare beforehand a metal pattern for the production of sand cylinders, put a mixture of thermo-setting resin and silica sand into the pattern and heat it, so as to produce sand cylinders having an outside and inside diameter of accurate size and a smooth outer and inner surface. The sand cylinders so produced are suflicient that even those of considerably small thickness and large diameter can be handled or pushed or inserted into the metal flask Without breakage or deformation. Preparation of a large number of such sand cylinders beforehand makes it possible to manufacture metal cylinders at a high rate of productivity.

As mentioned above, this invention utilizes the special characteristic of the sand mold made of thermo-setting resin to carry out the centrifugal casting of metal cylinders using such sand cylinders which are produced beforehand and which have an accurate, smooth surface. It utilizes the strength of the baked sand cylinder made by using phenolic resin, a thermo-setting resin, as a binder. The thickness of the sand cylinder is as little as 3-10 mm. It would be impossible to handle it if it had no such strength.

The following example relates to the use of a sand cylinder which is about 5 mm. thick consisting of phenolic resin, as a binder, and silica sand. The sand cylinder is inserted into the metal flask and held therein. For this purpose, too, it must be strong. The metal flask and the sand cylinder inserted therein combine to form the sand mold. The metal flask and the sand cylinder are not so close together that resin is fused to the flask but are so combined as to remain in contact. In the course of centrifugal casting, the metal flask protects the sand cylinder from breakage caused by centrifugal force, and transmits to the sand cylinder the rotation produced by the motor, which causes centrifugal force in the mold. As mentioned above, one of the special characteristics of this invention is that a sand cylinder is not formed inside the meal flask, but is pre-molded using a metal pattern outside the flask. This metal pattern consists of a body pattern which is made of steel and is so accurately finished that it has the same inside diameter as that of the metal flask, and a core pattern which is made of steel and is so accurately finished that it has the same outside diameter as that of the metal cylinder to be. produced by the centrifugal casting. These two pair of patterns are positioned on a common axis, leaving a space of 5 mm. between them. A mixture of thermo-setting resin and sand is poured into the space. Both patterns are constructed so that they can be heated to 150-200 C. by electricity, or the like. When they are heated for several seconds, the resin-sand mixture solidifies to form a sand cylinder. Then, these pattern molds are separated and the sand cylinder is removed. This sand cylinder is a sand mold having an inside and outside diameter with an accurate size and a smooth outer and inner surface, the same as that of the pattern. The sand cylinder is pushed into the metal flask having an accurately finished inner surface. The flask holds the sand cylinder firmly. They combine to form the centrifugal casting mold. While rotating the mold at a high speed in a horizontal position, molten metal is poured into the mold. The molten metal is subjected to centrifugal force and soon -solidifies and forms a metal cylinder.

Another special characteristic of this invention is that the sand cylinder does not adhere to the metal flask, which makes it unnecessary to use any force to separate the sand cylinder from the metal flask when taking the product out of the centrifugal casting mold. Metal cylinders can be stripped without resistance. Thus, the whole processes of centrifugal casting is accomplished with ease and effectiveness.

The following example relates to the centrifugal casting of cast iron pipe. Because cast iron pipe is the most popular shape for centrifugal casting, this disclosure will be the most understandable.

In the case of centrifugal casting of a cast iron pipe which is 150 mm. in inside diameter, 8 mm. thick and 4,000 mm. long, a metal pattern of the following specifications is used for the production of the sand cylinder for this purpose. The size of the body pattern metal is 156 mm. in inside diameter, 50 mm. thick and 500 mm. long. The inside of this pattern mold is accurately finished by machine. This mold consists of two parts which separate along lines parallel to the longitudinal axis. The size of the core mold is 150 mm. outside diameter, 25 mm. thick and 500 mm. long. Its outer surface is accurately finished. The body and the core molds are positioned on a common axis, leaving a space of 3 mm. between them. Before being positioned, they are sprayed with petroleum oil, which acts as a parting reagent, on the working surface. Both molds are heated to 150 C. by electricity, and then a resin-sand mixture is poured into the space. It will solidify in several seconds to form a sand cylinder. Then the electricity is cut olf. The core mold is pushed out, and the two parts of the body mold are separated and the sand cylinder is taken out. This sand cylinder has a smooth, accurate outer and inner surface and therefore is capable of use as a mold for precision casting.

Another special characteristic of this invention is that it enables production of a sand cylinder for a mold for precision casting using a mixture of resin and sand. The difference between a sand cylinder made by this invention and other generally-used shell molds is that the former has both the outer and the inner surfaces finished precisely, while the latter have either the outer or the inner surface so finished but have the other side rough just as it is formed by the spray of the resin-sand mixture. In order to accelerate the production of sand cylinders and the centrifugal casting job, the thickness of the sand cylinder should not be more than 10 mm., which constitutes a special characteristic of such a sand cylinder. This is because the speed of baking of a resin-sand mixture depends on the thickness of the sand cylinder to be made therefrom, and the speed of the solidifying of molten metal depends on the thickness of the sand cylinder and the heat insulation which it provides. In order to make a cast iron pipe having an inside diameter of 150 mm., there mustvbe prepared a metal flask having an accurately finished inside surface, an inside diameter of 156 mm., a length of 4,300 mm. and a thickness of 25 mm. Sand 4. cylinders made as described above, each having a length of about 500 mm. are inserted into the metal flask by using a hydraulic machine. To cover the whole length of the flask, eight sand cylinders will be required. .These.

sand cylinders are adhered to each other where they abut.

Thus, everything is ready for the centrifugal casting of.

cast iron pipe mm. in inside diameter using the precision casting sand mold firmly held by the metal flask.

This sand cylinder held in the flask is positioned in the centrifugalcasting machine, which will rotate the mold. When rotation is at the prescribed speed, molten cast iron is poured into the mold. This is all that is necessary for the centrifugal casting. When the cast iron pipe so produced gets cool, it is taken out of the fiask, together with the burnt sand cylinder, with almost no resistance. Cast iron pipes which are produced in this way, are so-called precision cast, having a smooth and straight surface and.

an accurate dimension. For the purpose of degassing the mold, the metal flask should hold the sand cylinder in such manner that a vacant space is produced between them. When molten metal is poured into a mold of this type, the gas which is generated in the sand cylinder can be easily and freely discharged into the space between the metal flask and the sand cylinder, and then into the air through a vent hole in the flaskor at the open ends of the mold. The gas, therefore, will not produce on the molten metal a back pressure which is harmful to cast pipe.

The mold of this type, therefore, is ideal for this purpose.

In FIG. 1 is shown a baked sand cylinder 1 of a thermosetting resin-sand mixture and by the use of a metal pat-1 tern. The sand cylinder has several projections 2 lying on the surface thereof and extending lengthwise (four projections are shown in this example). The cross section of the projection 2, as seen in FIG. 2,is a triangle or a similar shape.

diameter of the metal flask. FIG. 3 and FIG. 4 show the centrifugal casting mold ready for use, the sand cylinder 1 having been inserted into the metal flask 3. When the sand cylinder 1 is inserted into the metal flask 3, the sand cylinder is firmly held inside the metal flask by the projections 2, and the sand cylinder and the metal flask have the same axis, and a space 4 is left between them. Vent holes 7' are provided in the metal flask and open into the.

space 4 between the flask 3 and the sand cylinder 1.

Immediately after molten metal is poured into the sand.

cylinder 1 and the metal cylinder 8 is formed by .cen-

trifugal force produced by the rotation of the metal flask negligible. This mold, therefore, can be said to be ideal for this purpose.

One advantage of the mold of this type is that removal of the metal cylinders from the metal flask can be easily effected because of the space 4. Besides, there is no need for cleaning the gas vent which is always free of material.

Thus the present invention provides a way to carry out precision centrifugal casting of metal cylinders by using The whole course of a mold having a thin sand layer. the production can be accelerated by speedy mold production, casting and removal of the product.

low-cost equipment.

It is though that the invention and its advantages will be understood from the foregoing description andit is apparent that various changes may be made in the form,

The outside diameter 5 measured across the projections 2 is slightly greater than the inside The back pressure I produced by the gas in a mold of this type will be By using this invention, centrifugal casting of metal cylinders hav- I .ing a smooth surface and an accurate shape and size can 1 be effected at a high rate of productivity with simple,

construction and arrangement of the parts without departing from the spirit and scope of the invention or sacrificing its material advantages, the form hereinbefore described and illustrated in the drawings being merely a preferred embodiment thereof.

What is claimed is:

1. A sand cylinder for use in a centrifugal casting mold having a metal flask which is rotatable about the longitudinal axis thereof, said cylinder being made of a baked mixture of thermo-setting resin and silica sand and having a smooth accurate inner surface corresponding to the outer surface of the piece to be cast, and having a free outside surface spaced radially from the said inner surface with respect to the longitudinal axis thereof, and projection means on the outside surface thereof with the diameter of the sand cylinder measured across the extremities of said projection means being substantially the same as the inside diameter of the flask, whereby the sand cylinder can be inserted into the flask with the longitudinal axes thereof coaxial and a space will exist between the free outside surface of the sand cylinder and the inside surface of the flask.

2. A sand cylinder as claimed in claim 1 in which said projection means comprises a plurality of elongated projections extending along the length of said sand cylinder and equidistantly spaced around the periphery of the sand cylinder.

3. A centrifugal casting mold comprising a cylindrical flask, and at least one sand cylinder of a baked mixture of thermo-setting resin and silica sand and having a smooth accurate inner surface corresponding to the outer surface of the piece to be cast and having a free outside surface spaced radially from the said inner surface with respect to the longitudinal axis thereof, and projection means on the outside surface thereof, said sand cylinder positioned within said flask with the projection means engaged with the inside surface of the flask and holding said sand cylinder within said flask with the longitudinal axes thereof coaxial and keeping the outside surface of the sand cylinder spaced from the inside surface of the flask.

4. A centrifugal casting mold as claimed in claim 3 in which there are a plurality of said sand cylinders in said flask in end-to-end abutting relationship.

References Cited by the Examiner UNITED STATES PATENTS 1,681,085 8/1928 Beatty 22-113.5 1,777,673 10/ 1930 Kittredge 22-65 1,828,335 10/ 1931 Millspaugh 22-200.5 2,692,246 10/1954 Less 106-386 X 2,731,690 1/1956 Coupland et a1 22-200.5 2,770,857 11/1956 Boissou 22-113.5 X 2,919,479 1/1960 Menningen 22-134 X 2,943,068 6/1960 Freedman 106-386 X OTHER REFERENCES A.P.C. Application of Boissou, Ser. No. 474,770 published July 13, 1943.

J. SPENCER OVERHOLSER, Primary Examiner.

R. S. ANNEAR, Assistant Examiner. 

